1. Field
Certain embodiments relate to communication systems, such as Third Generation Partnership Project (3GPP) Long Term Evolution (LTE). More particularly, certain embodiments relate to a Range Expansion Bias (REB) reconfiguration method for LTE macro-pico Heterogeneous Networks (HetNets) in Authorized Shared Access (ASA)-aided spectrum sharing environments which can avoid causing harmful interference to any primary systems.
2. Description of the Related Art
With the evolution of LTE to LTE-advanced, carrier aggregation (CA) may be used to address wide bandwidth requirements. However, some operators have rather a limited amount of spectrum resources to be used for LTE, which conventionally makes it difficult to provide a high data rate for LTE systems. Therefore, some LTE systems are attempting to exploit more additional licensed spectrum as an extension of existing LTE licensed spectrum.
In one aspect, managing smaller cells (picocells, femtocells, and relays, etc.) in conventional macrocell networks is expected to provide better quality of service. With good deployment, capacity increases from low power nodes can be significantly improved. In another aspect, cognitive radio (CR) technology has been developed to allow unlicensed users to exploit spectrum opportunities from primary systems to enhance the spectrum utilization greatly. Authorized Shared Access (ASA) is a spectrum authorization scheme intended to solve spectrum scarcity on LTE band and spectrum under-utilization on additional licensed bands. ASA is intended to allow for a shared use of spectrum using cognitive radio technologies (for example, geo-location databases, sensing, and the like) based on an individual authorization model of spectrum rights, and can act as a regulatory enabler to making available, in a timely manner, harmonized spectrum for mobile broadband while overcoming time, resource and political constraints.
The introduction of picocells in a macro network may create an imbalance between the downlink and uplink coverage. The downlink coverage area of a Pico evolved Node B (PeNB) may be much smaller than that of a Macro evolved Node B (MeNB) due to factors such as low transmit power. However, the uplink coverage areas of different base stations (BSs) can be similar since the size of the coverage area may mainly depend on the user transmit power. On the other hand, PeNB resources may be not fully utilized due to the small number of pico users (PUE). To address these two issues, the 3GPP can use Cell Range Expansion (CRE) through biasing handover criteria between MeNBs and PeNBs on the same carriers. Using CRE, the cell association rule in the presence of picocells is based on the maximum downlink received power with a Range Expansion Bias (REB). This mechanism allows for flexible load balancing and sufficient resource utilization, and the REB values are configured by the MeNB to balance the traffic load between macrocell and picocell. Conventionally, the Almost Blank Subframe (ABS) is utilized to avoid inter-cell interference on both data and control channels of the downlink.